The invention herein described relates to a process for the preparation of herbicidal agents. More specifically it relates to an improved process for the preparation of certain o-carboxypyridylimidazolinones and o-carboxyquinolylimidazolinones.
Because the o-carboxypyridinyl- and o-carboxyquinolylimidazolinones of the present invention are excellent herbicidal agents, there is an ongoing search in the art for new and improved methods of preparing them. Unfortunately, the processes known in the art generally require excess starting material (e.g. the 2-quinaldine or 2-picoline precursor) or produce less than favorable yields or both. Additionally, in order to produce the desired end product some processes require many separate steps or require that less direct methods or circuitous routes be taken so that poor yields are avoided.
U.S. Pat. No. 4,474,962 describes a process for the condensation of substituted 2-picolines or 2-quinaldines with an aminocarboxamide and sulfur to form substituted 2-imidazolinylpyridines or 2-imidazlinylquinolines, respectively. However, this process requires the use of excess amounts of the 2-picoline or 2-quinaldine precursor to obtain goods yields of the corresponding 2-imidazolinylpyridine or quinoline product. In addition the best yields are obtained when the substituent in the 3 position of the 2-picoline or 2-quinaldine precursor is a hydrogen, thereby requiring the desired o-carboxylate functionality to be added in a separate sequential metallation/carboxylation step.
Commercially, the elimination of (1) excess starting material, (2) extra metallation/carboxylation steps and (3) low product yield would be significantly advantageous.
It is an object of this invention to provide a dramatic improvement in the process for the preparation of o-carboxypyridyl- and o-carboxyquinolylimidazolinones via a single step reaction which eliminates unnecessary extra steps and produces compounds of formula I in significantly increased yields while simultaneously reducing the use of excess amounts of reactants.